The state Opposition has called on the Premier to release advice on a possible legal challenge against the mining tax.

The Premier Colin Barnett yesterday indicated the State Government would support a High Court challenge, likely to be led by iron ore miner Fortescue Metals Group.

He says while the Government has received legal advice regarding the state's case, he will not release it until if, or when, a challenge is mounted.

Labor leader Mark McGowan has told the ABC he does not want public funds wasted.

"I wouldn't like to see the state go down the course of action of spending taxpayers' money like this if it was a waste of time," he said.

"So, I think it is important that we get to the bottom of whether there is a reasonable chance of success or whether this is using taxpayers' money in a wasteful manner."

Yesterday, Mr Barnett said the tax was discriminatory.

"It could be argued it discriminates between states, it could be argued that the tax is on a mineral resource, which constitutionally the Commonwealth government cannot tax, that belongs to the state," he said.

"That's part of the argument that would be mounted if a challenge comes on.

"If we have a case that would protect the revenue base of Western Australia into the future, that is in the state's interest."